Galactomannan gum thickeners are used to increase the viscosity of aqueous solutions or slurries such as oil well drilling fluids and fire retardant compositions and for modification and/or control of other rheological properties such as surface tension. When galactomannan gum-thickened aqueous compositions are stored for long periods of time, viscosity losses sometimes occur; and the losses are greater when such solutions are in contact with metals, apparently due to the destabilizing effect of ferrous ion. In order to extend the storage stability of galactomannan gum-thickened compositions, the use of certain salts and of heavy metal ions have been proposed. See U.S. Pat. Nos. 3,146,200 and 3,634,234. More recently, a soluble molybdenum compound and a mixture of molybdenum and a thiourea compound have been found to be useful as viscosity stabilizers. See U.S. Pat. Nos. 4,447,336 and 4,447,337.
Because of the fact that prior art viscosity stabilizers for galactomannan gum-thickened systems, have been known to exhibit characteristics which are incompatible with other additives or components and/or with the desired end uses, the discovery of additional stabilizers to provide broader utility would constitute a significant advance in the art and is an object of this invention.